This section introduces aspects that may help facilitate a better understanding of the disclosure. Accordingly, these statements are to be read in this light and are not to be understood as admissions about what is or is not prior art.
Ultrasound is a valuable diagnostic imaging technique for studying various areas of the body, including, for example, the vasculature, such as tissue microvasculature. Ultrasound provides certain advantages over other diagnostic techniques. For example, diagnostic techniques involving nuclear medicine and X-rays generally involve exposure of the patient to ionizing electron radiation. Such radiation can cause damage to subcellular material, including deoxyribonucleic acid (DNA), ribonucleic acid (RNA) and proteins. Ultrasound does not involve such potentially damaging radiation. In addition, ultrasound is relatively inexpensive relative to other diagnostic techniques, including CT and MRI, which require elaborate and expensive equipment.
Ultrasound involves the exposure of a patient to sound waves. Generally, the sound waves dissipate due to absorption by body tissue, penetrate through the tissue or reflect off of the tissue. The reflection of sound waves off of tissue, generally referred to as backscatter or reflectivity, forms the basis for developing an ultrasound image. In this connection, sound waves reflect differentially from different body tissues. This differential reflection is due to various factors, including the constituents and the density of the particular tissue being observed.
Ultrasound involves the detection of the differentially reflected waves, generally with a transducer that can detect sound waves having a frequency of one megahertz (MHZ) to ten MHZ. The detected waves can be integrated into an image which is quantitated and the quantitated waves converted into an image of the tissue being studied.
Ultrasound contrast agents are used to enhance the signal when imaging a patient using ultrasound. One interesting way to produce an ultrasound image is with a microbubble. Microbubbles are described as sphere or sphere-like ranging in size of greater than one micrometer, but smaller than one millimeter. Generally they are hollow with a gas core and vibrate when a sonic energy field is applied. The wave frequency emitted from the vibrating microbubble helps to produce an ultrasound image.
Another interesting use of a microbubble is to deliver a pharmaceutical agent to a tissue within the body. By encapsulating a pharmaceutical agent in a microbubble made up of a shell the pharmaceutical agent is delivered to a location prior to coming into contact with the cells and proteins which may alter its function, bioavailability, or concentration.
However, a drawback to the microbubbles and even nanobubbles currently known in the art is that they are too large and cumbersome for imaging or delivery of a therapeutic. What is needed is a smaller delivery mechanism that can travel into smaller vasculature and cross barriers between tissues and cells. More specifically it would be desirable to have a nanobubble that is small enough for imaging or delivery of a therapeutic. It would be further desirable if the nanobubble could be directed to the desired tissue and then have a therapeutic delivered at a specific time and place.